Over in this thread Jack said he'd added some further params suggested by papasi to the Ext.util.MixedCollection.each method, and indeed the latest source has those new params (index and length), but the docs still talk about the "first and only" parameter...

Ext.data.Store's "find" method has this in the summary at the top: "Returns a new collection that has been filtered." It actually returns the index of the record, or -1 (which it correctly says later under "Return").